Form follows finance. This is the unspoken motto of architects, and the guiding principle of property developers working in the City of London. Perhaps it always has been. As the recession appears to lighten, high-rise buildings, put on hold for the past months, are beginning to reach for the London cloudscape all over again.

Watered by fresh finance, the towers back in business include the hugely controversial "walkie-talkie" and the soaring "cheese-grater". Every City skyscraper has to have a pet name today. This gives it a kind of cuddly cartoon character and makes it seem more friendly than its true role as a machine for making, and losing, money in can ever really be.

The 180-metre-high walkie-talkie – so called since it looks more like an out-of-date mobile phone – is a bulky, concave structure rising up from the site of 20 Fenchurch Street. Its design, by the Uruguayan-born American architect Rafael Viñoly, was unveiled in 2006. After much protest, not least from English Heritage, it re-emerged slightly shorter, only to be held down by the collapse of the markets. Its saving grace is that it will boast a public roof garden, viewing gallery and restaurant, something few City towers have the grace to offer.

The cheese-grater, at 122 Leadenhall Street, is a more subtle design by Rogers Stirk Harbour, yet it is still enormous compared with recent City buildings. Resembling half a ziggurat, or at least half a ziggurat seen through a 21st-century lens, the 225-metre-high tower is an attempt to build as high as possible without imposing too forcefully on the views and baroque majesty of Wren's St Paul's Cathedral.

Even then, these Square Mile towers, along with the 288-metre-high "helter skelter" (aka the Pinnacle, or the Bishopsgate tower, designed by the American architects Kohn Pedersen Fox) and the 230-metre-high Heron tower – a "six-star office block" says its modest developer, Gerald Ronson – also by KPF, are to be overshadowed in 2012 by the "shard". This is the 310-metre-high skyscraper, designed by Renzo Piano, shooting up on the south side of London Bridge.

Behemoths all of them, but an architectural sign that the City of London is back in action doing what, for better or worse, it can't help itself doing: recreating itself like some monstrous phoenix made of gold coins. When you remember that the some of the buildings these new towers replaced were just 40 years old, the aim of the City is clear. Money. Above all else, and with buildings that look as much like giant pound and dollar signs on the London skyline as they do shards, cheese-graters, helter skelters or walkie-talkies.